Python Opencv学习笔记

GUI Features in OpenCV

Image 初步

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cv2.imread(const String & filename, int flags)

filename 图片名，字符串
flags 三种类型imread_color/grayscale/unchanged
如果图片不可以读入，则返回一个空矩阵。

cv2.imshow(const String & winname, InputArray mat)

winname 窗口名称
mat 要展示的图片的矩阵
Show with the function cv::Window_autosize
Always followed by the function cv::WaitKey

cv2.imwrite(const String & filename,InputArray img)

将要展示的图片输出到文件名为filename的文件

key = cv2.waitKey(int delayTime) & 0xFF

用于在键盘上读取输入
delayTime是反应时间
将返回值转换成ASCII码需要使用 & 0xFF

cv2.destoryAllWindows()
cv2.destoryWindow()

cv2.namedWindow(const String & winname, int flags=WINDOW_AUTOSIZE)

create a window with Window_autosize

Video初步

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cv2.VideoCapture()

import cv2 as cv

cap = cv.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Our operations on the frame come here
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv.imshow('frame',gray)
    if cv.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv.destroyAllWindows()

从摄像头获取视频信息

#用输出文件流对录制的文件信息进行保存
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc,20.0,(640,480))

import numpy as np
import cv2 as cv

cap = cv.VideoCapture(0)

# Define the codec and create VideoWriter object
fourcc = cv.VideoWriter_fourcc(*'XVID')
out = cv.VideoWriter('output.avi',fourcc, 20.0, (640,480))

while(cap.isOpened()):
    ret, frame = cap.read()
    if ret==True:
        #frame = cv.flip(frame,0)

        # write the flipped frame
        out.write(frame)

        cv.imshow('frame',frame)
        if cv.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break

# Release everything if job is finished
cap.release()
out.release()
cv.destroyAllWindows()

其中被我搞掉的那个是上下翻转的代码。
现在让我试验一下左右反转是否可行。
现在我发现了左右翻转只需要把其中的参数0改成1就可以了。是真的不知道这个作者为什么要在这里搞一个上下翻转，可能是笔者电脑自带的摄像头的问题。

Drawing初步

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cv2.line(InputOutputArray img,Point pt1,Point pt2,const Scalar & color,int thickness,int lineType,int shift)

lineType:

• filled
• cv2.line_4 4-connected line
• cv2.line_8 8-connected line
• cv2.line_AA antialiased line 反锯齿

cv2.circle()

cv2.rectangle(InputOutputArray img,Point pt1,Point pt2,const Scalar & color,int thickness,int lineType,int shift)

thickness can be made FILLED to fill the rect.

cv2.ellipse(InputOutputArray img,Point center,int radius,const Scalar & color,int thickness,int lineType,int shift)

thickness can be made FILLED to fill the circle.

cv.putText(InputOutputArray img, const String & 
text, Point org, int fontFace, double fontScale, 
Scalar color, int thickness = 1, 
int lineType = LINE_8, 
bool bottomLeftOrigin = false )

The parameter org means the left-bottom cornor of the text string.